The genus Lissoclinum of ascidians has proven to be an extremely rich source of novel biologically active natural products. Lissoclinum patella for example has yielded over twenty thiazole-containing cyclic peptides, three highly cytotoxic thiazole-containing macrolides and an antibacterial polyketide lactone (Nat. Prod. Rep., 1994, 11, 355 and earlier reports in the series). Another species, L. bistratum, has been reported to produce cyclic hexapeptides (Tetrahedron, 1992, 48, 341; and J. Org. Chem.(1992, 57, 6671), heptapeptides (Tetrahedron Lett. 1993, 2871) and two extremely toxic spiro ketal amides (see J. Med. Chem., 1989, 32, 1354; Tetrahedron, 1988, 44, 451; and J. Am. Chem. Soc., 1992, 114, 11 10). Lissoclinum (didemnum) voeltzkowi produces antileukemic cyclopentenones (J. Amer. Chem. Soc., 1988, 110, 1308) while L. vareau produces bright red heteroaromatic pigments (J. Org. Chem., 1989, 54, 4256) and a benzopentathiepin which is cytotoxic to human colon tumors (J. Amer. Chem. Soc., 1991, 113, 4709).